U.S. patent number 4,743,676 [Application Number 07/046,768] was granted by the patent office on 1988-05-10 for method for preparing polycarbonate of controlled molecular weight from aromatic bischloroformate.
This patent grant is currently assigned to General Electric Company. Invention is credited to Robert A. Pyles, James M. Silva.
United States Patent |
4,743,676 |
Silva , et al. |
May 10, 1988 |
Method for preparing polycarbonate of controlled molecular weight
from aromatic bischloroformate
Abstract
Linear polycarbonates of controlled molecular weight are
prepared by first reacting a bischloroformate composition with a
monohydroxyaromatic compound in a system comprising water, a base
and a suitable organic liquid, and then converting the resulting
partially capped bischloroformate composition to linear
polycarbonate by contact with an interfacial polycarbonate
formation catalyst in an alkaline medium. By this method, the
efficiency of the capping agent is improved.
Inventors: |
Silva; James M. (Clifton Park,
NY), Pyles; Robert A. (Evansville, IN) |
Assignee: |
General Electric Company
(Schenectady, NY)
|
Family
ID: |
21945288 |
Appl.
No.: |
07/046,768 |
Filed: |
May 7, 1987 |
Current U.S.
Class: |
528/371; 528/370;
528/372 |
Current CPC
Class: |
C08G
64/28 (20130101); C08G 64/06 (20130101) |
Current International
Class: |
C08G
64/00 (20060101); C08G 64/06 (20060101); C08G
64/28 (20060101); C08G 063/62 () |
Field of
Search: |
;528/371,372,370 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Anderson; Harold D.
Attorney, Agent or Firm: Pittman; William H. Davis, Jr.;
James C. Magee, Jr.; James
Claims
What is claimed is:
1. A method for preparing a linear aromatic polycarbonate of
controlled molecular weight which comprises the steps of:
(A) reacting an aromatic bischloroformate composition with a
monohydroxyaromatic compound or salt thereof in an essentially
phosgene-free reaction system also comprising water, a
substantially inert, substantially water-insoluble organic liquid
and an alkali or alkaline earth metal base, to produce a partially
capped bischloroformate composition; and
(B) contacting said partially capped bischloroformate composition
with an interfacial polycarbonate formation catalyst and an aqueous
alkali metal or alkaline earth metal base to form said linear
aromatic polycarbonate.
2. A method according to claim 1 wherein the aromatic
bischloroformate composition comprises compounds having the formula
##STR5## wherein R is a divalent aromatic radical; each Z is
independently H or ##STR6## at least one Z being ##STR7## and n is
from 0 to about 6.
3. A method according to claim 2 wherein step A is effected at a
temperature in the range of about 0.degree.-50.degree. C. and a pH
value of the aqueous phase in the range of about 2-11.5.
4. A method according to claim 3 wherein the organic liquid is
methylene chloride.
5. A method according to claim 4 wherein the amount of
monohydroxyaromatic compound or salt thereof is about 0.5-7.0 mole
percent, based on structural units in the bischloroformate
composition.
6. A method according to claim 5 wherein the monohydroxyaromatic
compound is phenol, p-t-butylphenol, p-cumylphenol, octylphenol,
nonylphenol or a salt thereof.
7. A method according to claim 5 wherein R has the formula
wherein each of A.sup.1 and A.sup.2 is a monocyclic divalent
aromatic radical and Y is a bridging radical in which one or two
atoms separate A.sup.1 from A.sup.2.
8. A method according to claim 7 wherein the base is at least one
of sodium hydroxide and calcium hydroxide and step B is effected at
a temperature in the range of about 20.degree.-50 20 C.
9. A method according to claim 8 wherein A.sup.1 and A.sup.2 are
each p-phenylene and Y is isopropylidene.
10. A method according to claim 9 wherein the monohydroxyaromatic
compound is phenol.
11. A method according to claim 9 wherein the monohydroxyaromatic
compound is p-t-butylphenol.
12. A method according to claim 9 wherein the monohydroxyaromatic
compound is p-cumylphenol.
13. A method according to claim 8 wherein step B is conducted at a
pH in the range of about 10-14 and the amount of catalyst employed
therein is in the range of about 0.025-3.0 mole percent based on
structural units in the bischloroformate composition.
14. A method according to claim 13 wherein the interfacial
polycarbonate formation catalyst is a tertiary amine, quaternary
ammonium or phosphonium salt or amidine.
15. A method according to claim 14 wherein the interfacial
polycarbonate formation catalyst is a trialkylamine.
16. A method according to claim 15 wherein the interfacial
polycarbonate formation catalyst is triethylamine.
17. A method according to claim 16 wherein A.sup.1 and A.sup.2 are
each p-phenylene and Y is isopropylidene.
18. A method according to claim 17 wherein the monohydroxyaromatic
compound is phenol.
19. A method according to claim 17 wherein the monohydroxyaromatic
compound is p-t-butylphenol.
20. A method according to claim 17 wherein the monohydroxyaromatic
compound is p-cumylphenol.
Description
This invention relates to the preparation of linear polycarbonates
from bischloroformate compositions. More particularly, it relates
to the preparation of linear polycarbonates of controlled molecular
weight.
The preparation of bischloroformate compositions and their
conversion to linear polycarbonates is known. Reference is made,
for example, to U.S. Pat. Nos. 3,646,102, 4,089,888 and 4,122,112,
and also to copending, commonly owned application Ser. No. 917,751,
filed Oct. 10, 1986.
In many procedures for the preparation of linear polycarbonates,
both from bischloroformate compositions and by the reaction of
phosgene with bisphenols, a monohydroxyaromatic compound is
frequently used as an agent for molecular weight control. Said
monohydroxyaromatic compound (hereinafter sometimes simply
designated "phenol" for brevity), when incorporated in minor
proportions in the reaction mixture, reacts with
chloroformate-terminated polymers to form inert aromatic end
groups, incapable of further polymerization.
Among the molecular species capable of so reacting with phenols are
chloroformate species of very low molecular weight. Phosgene itself
may also react when it is used in the synthesis of the
polycarbonate, yielding a diaryl carbonate such as diphenyl
carbonate.
It has been found that the presence in the product of diaryl
carbonates, as well as the presence of low molecular weight
polycarbonate oligomers, may cause difficulties in molding
operations. These include problems in removing molded polycarbonate
articles from the mold, in producing parts using rapid cycle times,
and in producing parts without physically or optically flawed
surfaces. Such problems can be particularly vexatious when
regularity of shape of such molded articles is a prime concern,
such as in the molding of optical disks.
It has also been discovered that conventional methods for preparing
linear polycarbonates from phosgene or bischloroformate
compositions are relatively inefficient in their utilization of
phenols introduced for molecular weight control. The average
molecular weight of the polycarbonate is frequently higher than
would be expected, considering the amount of phenol present. The
reasons for this phenomenon are not fully understood, but it is
possible that the phenol does not completely react or that it
reacts preferentially with very low molecular weight species,
producing oligomers which do not materially contribute to the
weight average molecular weight of the polycarbonate product.
The present invention provides a method for linear polycarbonate
preparation with improved incorporation of phenols used for
molecular weight control. As a result of this improved
incorporation, a lower proportion of phenol is necessary for the
production of a polycarbonate with a given average molecular
weight. The invention also produces polycarbonate products
containing no detectable diaryl carbonate and having the potential
for insignificant or very low proportions of low molecular weight
oligomers, thus minimizing molding problems of the type previously
described.
The invention is a method for preparing a linear aromatic
polycarbonate of controlled molecular weight which comprises the
steps of:
(A) reacting an aromatic bischloroformate composition with a
monohydroxyaromatic compound or salt thereof in a reaction system
also comprising water, a substantially inert, substantially
water-insoluble organic liquid and an alkali or alkaline earth
metal base, to produce a partially capped bischloroformate
composition; and
(B) contacting said partially capped bischloroformate composition
with an interfacial polycarbonate formation catalyst and an aqueous
alkali metal or alkaline earth metal base to form said linear
aromatic polycarbonate.
The aromatic bischloroformate compositions utilized in the method
of this invention comprise compounds having the formula ##STR1##
wherein R is a divalent aromatic radical; each Z is independently H
or ##STR2## at least one Z being ##STR3## and n is 0 or a positive
number. They usually comprise principally bischloroformates (i.e.,
each Z is ##STR4## having varying molecular weight. It is often
desirable to maximize the proportion of bischloroformates in which
n is from 0 to about 6, at the expense of higher bischloroformates,
monochloroformates, unreacted dihydroxyaromatic compounds and other
by-products. It is also necessary that the bischloroformate
composition be essentially phosgene-free; if phosgene is present,
it will react with the phenol to form diaryl carbonate, whose
presence is disadvantageous as noted hereinabove.
These bischloroformate compositions may be prepared by known
methods by the reaction of phosgene with dihydroxyaromatic
compounds having the formula
The R values may be aromatic hydrocarbon or substituted aromatic
hydrocarbon radicals, with illustrative substituents being alkyl,
cycloalkyl, alkenyl (e.g., crosslinkable-graftable moieties such as
allyl), halo (especially fluoro, chloro and/or bromo), nitro and
alkoxy.
The preferred R values have the formula
wherein each of A.sup.1 and A.sup.2 is a monocyclic divalent
aromatic radical and Y is a bridging radical in which one or two
atoms separate A.sup.1 from A.sup.2. The free valence bonds in
formula III are usually in the meta or para positions of A.sup.1
and A.sup.2 in relation to Y.
In formula III, the A.sup.1 and A.sup.2 values may be unsubstituted
phenylene or substituted derivatives thereof wherein the
substituents are as defined for R. Unsubstituted phenylene radicals
are preferred. Both A.sup.1 and A.sup.2 are preferably p-phenylene,
although both may be o- or m-phenylene or one o- or m-phenylene and
the other p-phenylene.
The bridging radical, Y, is one in which one or two atoms,
preferably one, separate A.sup.1 from A.sup.2. It is most often a
hydrocarbon radical and particularly a saturated C.sub.1-12
aliphatic or alicyclic radical such as methylene,
cyclohexylmethylene, [2.2.1]bicycloheptylmethylene, ethylene,
ethylidene, 2,2-propylidene, 1,1-(2,2-dimethylpropylidene),
cyclohexylidene, cyclopentadecylidene, cyclododecylidene or
2,2-adamantylidene, especially an alkylidene radical.
Aryl-substituted radicals are included, as are unsaturated radicals
and radicals containing atoms other than carbon and hydrogen; e.g.,
oxy groups. Substituents such as those previously enumerated may be
present on the aliphatic, alicyclic and aromatic portions of the Y
group.
The following dihydroxyaromatic compounds are illustrative:
Resorcinol
4-Bromoresorcinol
Hydroquinone
4,4'-Dihydroxybiphenyl
1,6-Dihydroxynaphthalene
2,6-Dihydroxynaphthalene
Bis(4-hydroxyphenyl)methane
Bis(4-hydroxyphenyl)diphenylmethane
Bis(4-hydroxyphenyl)-1-naphthylmethane
1,1-Bis(4-hydroxyphenyl)ethane
1,2-Bis(4-hydroxyphenyl)ethane
1,1-Bis(4-hydroxyphenyl)-1-phenylethane
2,2-Bis(4-hydroxyphenyl)propane ("bisphenol A")
2-(4-Hydroxyphenyl)-2-)3-hydroxyphenyl)propane
2,2-Bis(4-hydroxyphenyl)butane
1,1-Bis(4-hydroxyphenyl)isobutane
1,1-Bis(4-hydroxyphenyl)cyclohexane
1,1-Bis(4-hydroxyphenyl)cyclododecane
Trans-2,3-bis(4-hydroxyphenyl)-2-butene
2,2-Bis(4-hydroxyphenyl)adamantane
.alpha..alpha.'-Bis(4-hydroxyphenyl)toluene
Bis(4-hydroxyphenyl)acetonitrile
2,2-Bis(3-methyl-4-hydroxyphenyl)propane
2,2-Bis(3-ethyl-4-hydroxyphenyl)propane
2,2-Bis(3-n-propyl-4-hydroxyphenyl)propane
2,2-Bis(3-isopropyl-4-hydroxyphenyl)propane
2,2-Bis(3-sec-butyl-4-hydroxyphenyl)propane
2,2-Bis(3-t-butyl-4-hydroxyphenyl)propane
2,2-Bis(3-cyclohexyl-4-hydroxyphenyl)propane
2,2-Bis(3-allyl-4-hydroxyphenyl)propane
2,2-Bis(3-methoxy-4-hydroxyphenyl)propane
2,2-Bis(3,5-dimethyl-4-hydroxyphenyl)propane
2,2-Bis(2,3,5,6-tetramethyl-4-hydroxyphenyl)propane
2,2-Bis(3-5-dichloro-4-hydroxyphenyl)propane
2,2-Bis(3,5-dibromo-4-hydroxyphenyl)propane
2,2-Bis(2,6-dibromo-3,5-dimethyl-4-hydroxyphenyl)propane
.alpha.,.alpha.-Bis(4-hydroxyphenyl)toluene
.alpha.,.alpha.,.alpha.',.alpha.'-Tetramethyl-.alpha.,.alpha.'-bis(4-hydrox
yphenyl)-p-xylene
2,2-Bis(4-hydroxyphenyl)hexafluoropropane
1,1-Dichloro-2,2-bis(4-hydroxyphenyl)ethylene
1,1-Dibromo-2,2-bis(4-hydroxyphenyl)ethylene
1,1-Dichloro-2,2-bis(5-phenoxy-4-hydroxyphenyl)ethylene
4,4'-Dihydroxybenzophenone
3,3-Bis(4-hydroxyphenyl)-2-butanone
1,6-Bis(4-hydroxyphenyl)-1,6-hexanedione
Ethylene glycol bis(4-hydroxyphenyl) ether
Bis(4-hydroxyphenyl) ether
Bis(4-hydroxyphenyl) sulfide
Bis(4-hydroxyphenyl) sulfoxide
Bis(4-hydroxyphenyl) sulfone
Bis(3,5-dimethyl-4-hydroxyphenyl) sulfone
9,9-Bis(4-hydroxyphenyl)fluorene
2,7-Dihydroxypyrene
6,6'-Dihydroxy-3,3,3',3'-tetramethylspiro (bis)indane
("spirobiindane bisphenol")
3,3-Bis(4-hydroxyphenyl)phthalide
2,6-Dihydroxydibenzo-p-dioxin
2,6-Dihydroxythianthrene
2,7-Dihydroxyphenoxathiin
2,7-Dihydroxy-9,10-dimethylphenazine
3,6-Dihydroxydibenzofuran
3,6-Dihydroxydibenzothiophene
2,7-Dihydroxycarbazole.
Bisphenol A (in which Y is isopropylidene and A.sup.1 and A.sup.2
are each p-phenylene) is often especially preferred for reasons of
availability and particular suitability for the purposes of the
invention.
Also useful are bisphenols containing ester linkages. These may be
prepared, for example, by reacting two moles of bisphenol A with
one mole of isophthaloyl or terephthaloyl chloride.
As previously explained, the molecular weight control agent used
according to the invention is a phenol or similar
monohydroxyaromatic compound. Compounds of this type useful to
regulate the molecular weight of polycarbonate are known in the
art; examples are phenol, p-t-butylphenol, p-cumylphenol,
octylphenol and nonylphenol. Phenol is often preferred by reason of
its low cost, availability and effectiveness.
Introduction of the phenol into the reaction mixture may be
effected neat or in aqueous or organic solution. If desired, it may
be introduced as a salt, most often an alkali metal salt.
Also employed in step A of the method of this invention are water,
an inert organic liquid and an alkali or alkaline earth metal base.
Said organic liquid should also be substantially insoluble in
water. Illustrative liquids are aliphatic hydrocarbons such as
hexane and n-heptane; chlorinated aliphatic hydrocarbons such as
methylene chloride, chloroform, carbon tetrachloride,
dichloroethane, trichloroethane, tetrachloroethane, dichloropropane
and 1,2-dichloroethylene; aromatic hydrocarbons such as benzene,
toluene and xylene; substituted aromatic hydrocarbons such as
chlorobenzene, o-dichlorobenzene, the chlorotoluenes, nitrobenzene
and acetophenone; and carbon disulfide. The chlorinated aliphatic
hydrocarbons, especially methylene chloride, are preferred.
The alkali or alkaline earth metal base is most often a hydroxide
such as sodium hydroxide, potassium hydroxide or calcium hydroxide.
In relatively small scale reactions, especially those conducted
batchwise, calcium hydroxide may be preferred since its limited
solubility aids in stabilizing the pH in the range of about
11.8-12.3. Carbonates and bicarbonates may also be employed and
frequently provide a degree of buffering which may be
advantageous.
Sodium and potassium hydroxides, and especially sodium hydroxide,
are often preferred on a larger scale because of their relative
availability and low cost. Their use requires a relatively high
flow rate in the vicinity of pH monitoring means such as pH
electrodes, to prevent fouling. Frequent reference to sodium
hydroxide will be made hereinafter, but the invention is obviously
not limited thereto.
Formation of the partially capped bischloroformate composition in
step A may be effected under any interfacial reaction conditions
suitable for the reaction of chloroformates with hydroxyaromatic
compounds. Thus, contact of the phenol with the bischloroformate
composition may, for example, involve temperatures in the range of
about 0.degree.-50.degree. C. and pH values of the aqueous phase in
the range of about 2-11.5. Time periods may be from a few seconds
to 20 minutes or more; longer time periods are not harmful, but
times greater than about 30 minutes ordinarily provide no
discernible advantage. Suitable conditions are known to those
skilled in the art and/or may be determined by simple
experimentation. At low pH values, it may frequently be necessary
to conduct the reaction over a relatively long time period and/or
at relatively high temperatures, exemplified by the reflux
temperature of methylene chloride (about 40.degree. C.). When the
pH is high, on the other hand, lower temperatures and/or shorter
reaction times may be advisable to avoid hydrolysis of
chloroformate groups.
The proportion of phenol with respect to bischloroformate will
depend on the desired molecular weight and/or intrinsic viscosity
of the linear polycarbonate product. In general, lower amounts of
phenol are required according to the present invention than in
interfacial polymerizations or in bischloroformate polymerization
wherein the phenol is first introduced during the polymerization
reaction. Phenol amounts of about 0.5-7.0 mole percent, based on
structural units in the bischloroformate composition, are
typical.
The product of step A is a partially (generally about 2-5 mole
percent) capped bischloroformate composition wherein by far the
greater proportion of the capped molecules are monocapped and
therefore still reactive at one end. Dicapped molecules would, of
course, be inert to further reaction and would have a low molecular
weight compared to that of the linear polycarbonate desired as the
ultimate product of the method of this invention. Thus, such
molecules if present in substantial proportions might skew
molecular weight determinations and also cause molding difficulties
such as those previously described. It has been discovered,
however, that the proportion of dicapped species in the partially
capped bischloroformate composition is not high enough to give rise
to these problems.
In step B, the partially capped bischloroformate composition is
contacted with an interfacial polycarbonate formation catalyst and
further aqueous alkali metal or alkaline earth metal base. Such
contact most often takes place in the presence of the organic
liquid from step A, and is therefore heterogeneous. Also present
may be at least one bisphenol of formula II or salt thereof.
As interfacial polycarbonate formation catalysts, there may be
used, for example, the tertiary amines disclosed in U.S. Pat. Nos.
4,217,438 and 4,368,315, the disclosures of which are incorporated
by reference herein. They include aliphatic amines such as
triethylamine, tri-n-propylamine, diethyl-n-propylamine and
tri-n-butylamine and highly nucleophilic heterocyclic amines such
as 4-dimethylaminopyridine (which, for the purposes of this
invention, contains only one active amine group). The preferred
amines are those which dissolve preferentially in the organic phase
of the reaction system; that is, for which the organic-aqueous
partition coefficient is greater than 1. This is true because
intimate contact between the amine and bischloroformate composition
is essential for polycarbonate formation. For the most part, such
amines contain at least about 6 and preferably about 6-14 carbon
atoms.
The most useful amines are trialkylamines containing no branching
on the carbon atoms in the 1- and 2-positions. Especially preferred
are tri-n-alkylamines in which the alkyl groups contain up to about
4 carbon atoms. Triethylamine is most preferred by reason of its
particular availability, low cost, and effectiveness. Also useful
are quaternary ammonium and phosphonium salts and amidines of the
type known in the art to be effective in the reaction of phosgene
with bisphenols.
In general, the polycarbonate formation reaction may be conducted
at a temperature in the range of about 0.degree.-100.degree. C. and
preferably about 20.degree.-50.degree. C.; at a pH in excess of
about 10, preferably in the range of about 11-14; and using an
amount of catalyst within the range of about 0.025-3.0 mole percent
based on structural units in the bischloroformate composition.
Either batch or continuous conditions may be used for the method of
this invention, or one step may be conducted batchwise and the
other continuously. If step A is conducted batchwise, all residual
phosgene should first be destroyed by conventional methods.
Continuous methods employable in step B include those described in
the aforementioned patents and copending application, the
disclosures of which are incorporated by reference herein.
The reasons for the decrease in phenol required for molecular
weight control according to the present invention are not fully
understood. A possible factor is relatively slow migration of
phenol from aqueous to organic phase during polycarbonate formation
by prior art methods, as compared to the relatively rapid
polycarbonate-forming reaction. In the present invention, on the
other hand, no competing polymerization takes place during step A
and capping can go essentially to completion prior to initiation of
polymerization during step B. The invention is, of course, in no
way dependent on theory.
The invention is illustrated by the following examples.
Polycarbonate molecular weights are weight average molecular
weights determined by gel permeation chromatography. Intrinsic
viscosities were measured in chloroform at 25.degree. C.
EXAMPLE 1
A 500-ml. Morton flask fitted with a stirrer, reflux condenser and
thermometer was charged with 150 ml. of deionized water, 1 gram of
sodium bicarbonate, 225 mg. (2.4 mmol.) of phenol and 100 ml. of a
bisphenol A bischloroformate composition containing 100 mmol. of
total bisphenol A structural units and corresponding roughly in
molecular weight to the dimer. The mixture was stirred for 20
minutes as 50% aqueous sodium hydroxide solution was added to
maintain the pH at 8.5. At the end of that time, analysis of the
organic phase by gel permeation chromatography showed no remaining
phenol.
Calcium hydroxide, 15 grams, was added to the mixture and a
solution of 101 mg. (1 mmol.) of triethylamine in 10 ml. of
methylene chloride was introduced at a constant rate over 5
minutes, during which time the reaction mixture reached the reflux
temperature. Stirring was continued for an additional 25 minutes,
after which the organic phase was separated, washed repeatedly with
aqueous acid and water and evaporated to yield the linear
polycarbonate.
Duplicate products made by this procedure were compared in
molecular weight to control products prepared by a similar process
in which the phenol and triethylamine were added concurrently to
the mixture of bischloroformate solution and water. The products
prepared by the method of the invention had molecular weights of
33,300 and 29,300, as compared with 41,800 and 50,400 for the
controls. Thus, the method of this invention utilizes phenol
substantially more efficiently than the controls, to produce a
polycarbonate of lower molecular weight
EXAMPLE 2
A 1-liter Morton flask fitted with a stirrer, a reflux condenser, a
pH electrode and tubes for addition of phosgene (dip tube) and
sodium hydroxide solution was charged with 57 grams (250 mmol.) of
bisphenol A, 250 ml. of methylene chloride and 250 ml. of water.
Phosgene was passed through the mixture at 25.degree. C., with
stirring, for 2 hours at 610 mg. per minute (total 739.4 mmol.), as
25% aqueous sodium hydroxide solution was added to maintain a pH of
8.5. The mixture was stirred at this pH for an additional 20
minutes, after which there were added 125 ml. of water and 340 mg.
(2.3 mmol.) of p-t-butylphenol. Stirring was continued for 5
minutes, after which additional base was introduced to increase the
pH to 12 and a solution of 250 mg. (2.48 mmol.) of triethylamine in
5 ml. of methylene chloride was added over 5 minutes. The mixture
was stirred for an additional 30 minutes, after which the
polycarbonate product was isolated as in Example 1. It had an
intrinsic viscosity of 0.62 dl./g.
A similar polycarbonate was prepared by passing phosgene at 950 mg.
per minute for 30 minutes (total 287.9 mmol.) into a mixture of
bisphenol A, methylene chloride and triethylamine in the above
amounts, 125 ml. of water and 530 mg. (3.53 mmol.) of
p-t-butylphenol. The pH was maintained at 10.5 by the addition of
25% aqueous sodium hydroxide solution. The resulting polycarbonate
also had an intrinsic viscosity of 0.62 dl./g. Thus, substantially
less p-t-butylphenol was required according to the method of this
invention than in a conventional interfacial polymerization
procedure.
* * * * *